1. Field of the Invention
This invention relates to a structure for partially oxidizing fuel in an intake system of a homogeneous-charge compression-ignition (HCCI) engine.
2. Discussion of the Related Art
The homogeneous-charge compression-ignition engine is a relatively new type of engine. It has certain benefits that are attractive such as extremely low NOx emissions due to the low combustion temperatures of the diluted mixture and zero soot emissions due to the premixed lean mixture. Also, thermal efficiency of the HCCI engine is much higher than SI engines and is comparable to conventional CI engines due to the high compression ratio (similar to diesel engines), un-throttled operation (minimizing engine pumping losses), high air fuel ratio (high specific heat ratio), reduced radiation heat transfer loss (without sooting flame), and the low cycle-by-cycle variation of HCCI combustion (since the early flame development and the combustion rate of the HCCI engine does not rely on in-cylinder flow and turbulence).
The difficulty with combustion in an HCCI engine is controlling the ignition timing and the combustion rate at different operating conditions. This is because combustion starts by auto-ignition when the mixture reaches a certain temperature. Thus, the fuel-air mixture is formed much earlier before top dead center (TDC), and ignition can occur at any time during the compression process. Thus as the engine load increases, the ignition tends to advance, and the combustion rate tends to increase due to the richer mixture. The thermal efficiency may also decrease due to early heat release before TDC, and the engine becomes rough due to fast and early combustion.
When the engine load decreases, ignition tends to be retarded which may eventually result in misfire as well as an increase in HC and CO emissions. When engine speed increases, the time for the main heat release tends to be retarded since the time available for low-temperature preliminary reaction of the diluted mixture becomes insufficient and misfiring may occur.
An object of this invention is to provide a device that assists in controlling the ignition timing and the combustion rate at different operating conditions in an HCCI engine.
It is a further object of the invention to provide a device in an intake system of an HCCI engine that can partially oxidize fuel prior to entering a combustion chamber.
It is yet another object of the present invention to provide an intake system of an HCCI engine with a device that can allow controllable combustion with slow burning and fast quenching.
It is still a further object of the present invention to provide a method of producing partially oxidized fuel through a low-temperature chain propagating reaction prior to entering the combustion chamber of an HCCI engine.
It is another object of the present invention to provide a device and method for partially oxidizing fuel to promote autoignition in HCCI combustion so as to expand the range of HCCI combustion during light load, high speed and engine cold start.
The above objects are achieved, and the prior approaches are overcome by an oxidation device for partially combusting a quantity of fuel prior to a combustion chamber in a homogeneous charge compression ignition engine. The device comprises a housing including a fuel inlet, an air inlet and an outlet; a source of ignition attached to the housing for causing ignition of a portion of a fuel-air mixture supplied to the housing; and rapid quenching means for quickly extinguishing a combustion flame in the fuel-air mixture following ignition.
The objects of the invention are also accomplished by a homogeneous charge compression ignition engine comprising an air intake passage; a combustion chamber connected to the air intake passage; a fuel inlet for providing fuel to be partially oxidized prior to entering the combustion chamber, the fuel inlet being disposed in said air intake passage; and a glow plug disposed in the air intake passage for heating the fuel and causing it to react without complete combustion prior to entering the combustion chamber.
The objects of the invention are also accomplished by a homogeneous charge compression ignition engine comprising an air intake passage, a combustion chamber connected to the air intake passage, and a partial oxidation device. The partial oxidation device comprises a housing including a fuel inlet, an air inlet, an outlet, a mixing chamber and a burning chamber. The air inlet is connected to the air intake passage and the outlet is also connected to the air intake passage. A source of ignition is attached to the housing for causing ignition of a portion of a fuel-air mixture supplied to the housing. A partially oxidized fuel is produced as the combusting fuel-air mixture is rapidly quenched upon exiting the outlet of the housing and entering the air intake passage.
With these structures, it is possible to promote autoignition of HCCI combustion. This allows the range of HCCI combustion at light loads, high speeds and during engine cold start to be expanded.